This invention relates to positioning systems for vehicles, and in particular, to a system for positioning a vehicle at a storage bin for automatic storage and retrieval.
Automatic storage and retrieval systems are utilized in warehousing to provide maximum efficiency and economy of operation for material handling. An increasing trend toward automation of materials handling functions in warehouses has occured in conjunction with the use of larger storage racks. Such storage racks may, for example, be constructed to heights of 85 feet or more and of virtually unlimited length. A principal advantage to constructing such storage racks to greater heights is that the building floor area required to store an equivalent amount of material is thereby reduced in comparison to a system of lesser height.
Vehicles are used in such warehouses for moving material loads therein, for example in storage operations for movement from pickup stations to designated storage bins and in retrieval operations for movement from storage bins to pickup stations. The positioning mechanisms for guiding such vehicle movements must be capable of consistently and accurately positioning a vehicle within a sufficiently precise location at a storage bin for performing a storage or retrieval operation of a material load in a minimum amount of time.
Such positioning mechanisms are also preferably capable of receiving a command and thereby automatically causing a vehicle to perform desired operations at a designated storage bin and pickup or discharge station. Such a command, for example, might direct a vehicle to move to a predetermined storage bin, retrieve a material load therefrom, move to a discharge station or another predetermined storage bin, and discharge the load thereat. Thus, with such an automatically controlled warehouse, an operator can store and retrieve material merely by inputting the proper command, for example, by means of a keyboard or card data system.
A further advantage of automatic storage and retrieval systems is that, because an operator is not required on each vehicle, the environment within which the storage rack is positioned need not be controlled for the safety and comfort of an operator. Thus, for example, refrigerated good may be stored at low temperatures with the operator positioned outside the freezer or cooler. Also, a relatively low cost, unheated and uncooled warehouse type structure may be provided for the storage rack with the operator remotely positioned therefrom in a more controlled environment.
To achieve such automated operation, a positioning mechanism is required to accurately place a vehicle in a predetermined location with respect to a designated storage bin. A variety of such mechanisms have been developed for use in such automatic storage and retrieval systems. A number of such heretofore conventional positioning mechanisms utilize a counter associated with various controls for stopping vehicle travel upon receiving a predetermined number of signals or impulses from the counter. For example, the Lemelson U.S. Pat. No. 3,285,437 shows a switch attached to a carrier or vehicle and tripped by engaging pins, cut-outs or dogs along an overhead track, each corresponding to a column of storage bins. However, such mechanical tripping devices are susceptible to damage which may result in counter error and the vehicle attempting to deposit or retrieve a load at the wrong storage bin. Such attempts can result in collisions between material loads on the vehicle and material loads already positioned at the mistakenly selected bin with resultant damage to each.
A different method of actuating a counter is shown in the Lemelson U.S. Pat. No. 3,486,640 which utilizes reflectors attached to a storage frame. Light sources and photoelectric scanners are provided on a carrier for detecting the reflectors and actuating the counter to determine when a required distance has been traversed. Such photoelectric systems are also susceptible to misdirecting a carrier if, for example, a reflector is so dulled that the passing sensor is not actuated or if the sensor is mistakenly actuated by other reflective material adjacent its path such as a reflective portion of a material load. A further example of a tripping mechanism connected to a counter is disclosed in the Saul U.S. Pat. No. 3,402,835 and includes a magnetic proximity switch connected to the carrier and actuated by metallic posts positioned adjacent respective columns of storage bins. However, each of the discussed prior art positioning mechanisms which utilize counters responding to individual rows or columns of storage bins are susceptible to miscalculating the position of a vehicle or carrier and thereby causing damage as described above.
In addition to their susceptibility to positioning errors, counting systems typically utilize stepping relays which must be individually pulsed to the number of a designated storage bin. Thus, the required circuitry tends to be especially complex for storage systems having relatively large numbers of bins.
Another type of positioning mechanism utilizing a counter is shown in the Richins U.S. Pat. No. 3,572,484 and the Cassel U.S. Pat. No. 3,799,057, both of which disclose an encoder driven by a wheel of a carriage and generating a predetermined number of electrical pulses for each rotation thereof. The pulses are then counted by stepping relays until a predetermined number have been received designating the carriage in a predetermined position. An inherent disadvantage with such positioning mechanisms is that the storage bins must be evenly spaced so that the dimensions of each represent the same number of carriage wheel revolutions. Thus, warehouses utilizing such a positioning mechanism are not especially suited for use with storage bin loads having different sizes. Also, the spacing of storage bins within most warehouses is interrupted with columns and other support structure which makes even spacing of the storage bins impractical.
The DeBrey U.S. Pat. No. 3,402,836 shows a positioning mechanism which attempts to avoid some of the difficulties inherent with such mechanisms using counting type systems. The storage bins shown therein each have a coded array of photoelectric targets which, when detected by photoelectric sensors, uniquely identify each storage bin. However, a storage rack having hundreds of individual storage bins, for example, would also require a like number of unique arrays of reflective markers and a complex system of photoelectric sensors for uniquely identifying each respective storage bin. Another non-counting type of positioning mechanism is shown in the Macko U.S. Pat. No. 3,486,092 which includes bridge network circuitry with a variable resistance leg and polarity sensitive means on the carrier responding to an imbalance of the bridge and initiating carrier movement in the proper direction. The carrier is properly positioned when the bridge balanced. Disadvantages of such a positioning mechanism include difficulties with varying the resistance sufficiently in a relatively long storage rack and the difficulty of positioning a carriage accurately enough for storage and retrieval operations which often have tolerances of fractions of an inch.
Therefore, prior art automatic warehouse positioning systems have tended to be susceptible to positioning errors, excessively complex in structure and circuitry, and not well adapted for use with relatively long storage racks.
The present invention comprises a positioning mechanism wherein rough positioning within a zone at a designated storage bin is accomplished with an encoder generating a signal the value of which varies in response to movement of the vehicle. Fine positioning of the vehicle is accomplished with signal generating means designating a predetermined location of the vehicle within each zone. Control means receives the signals and causes the vehicle to move to the zone and to stop at the predetermined location.